As is known in the art, a phased array antenna includes a plurality of antenna elements spaced apart from each other by known distances. Each of the antenna elements are coupled through a plurality of phase shifter circuits, amplifier circuits and/or other circuits to either or both of a transmitter or receiver. In some cases, the phase shifter, amplifier circuits and other circuits (e.g. mixer circuits) are provided in a so-called transmit/receive (T/R) module and are considered to be part of the transmitter and/or receiver.
The phase shifters, amplifier and other circuits (e.g. T/R modules) often require an external power supply (e.g. a DC power supply) to operate correctly. Thus, the circuits are referred to as “active circuits” or “active components.” Accordingly, phased array antennas which include active circuits are often referred to as “active phased arrays.”
Active circuits dissipate power in the form of heat. Thus, active phased arrays must be cooled.
In active phased arrays having T/R channels which use relatively little power (i.e. less than two Watts (W) average RF power), individual finned heat-sinks (or “hat-sinks”) are attached to each active circuit. That is, each active circuit has an individual heat sink attached thereto. Although this approach may satisfy the cooling requirements for the active phased array, this thermal management system is expensive since the cost of disposing a “hat-sink” on an active circuit is on the same order as the cost of the active circuit itself.
Furthermore, active phased arrays having an aperture size greater than about one square meter (m2), typically operate at relatively high power levels (i.e. greater than two Watts average RF power). In this case, large capacity blowers are required to force air across the hat sinks. The use of such large capacity blowers results in the need for a relatively complicated air supply and return manifold and also causes high levels of backpressure across the phased array. Thus, the hat sink approach to air-cooling such active phased arrays is relatively difficult to implement and is also difficult to scale up to apertures greater than one square meter.
If large blowers are not used in relatively high power per T/R channel applications, it is often necessary to use a liquid cooling approach to maintain active circuits in their normal operating temperature range. Although the liquid cooling approach is effective to maintain active circuits at temperatures at or below maximum allowed operating temperatures, liquid cooling has very high life cycle costs. For example, liquid cooling requires the use of a manifold through which the liquid circulates. Such liquid filled manifolds add a tremendous amount of weight and complexity to a radar system which increases the radar system recurring cost and also increases the transportation costs and maintenance costs over the operational life of the active phased array.
It would therefore, be desirable to provide a reliable and cost effective technique for cooling RF systems which operate over a wide range of RF output power levels. It would also be desirable to provide a reliable and cost effective system and technique for cooling active phased arrays which operate over a wide range of RF output power levels.